Timing signal generation is of vital application in digital circuits. Devices in the circuits are operated according to the timing signal to ensure the correct timing of signal transfer and other interactions. A timing generator capable of generating a stable and accurate periodic pulse signal provides a reliable reference for the operation of the circuits.
The timing generator of early years is realized by employing a clocking source, such as a crystal oscillator or quartz oscillator. The crystal oscillator provides high frequency and stable clock wave or periodic pulses with accurate timing. However, the clocking pulses are generated by the resonance effect with a fixed frequency. Thus, the frequency of the timing signal is limited by the fixed frequency and only frequencies that are multiples of the fixed frequency. With the various designs and operation modes of the circuits, the application is quite limited when the designed operating frequency of the circuit is not matched.
Many circuits have been proposed for providing selectable and adjustable frequencies of the timing signal. Devices like capacitors, flip-flop' s, inverters, and comparators are widely applied and combined to form timing signal generators. A timing generator has to operate continuously once the power is supplied to set the circuit into operation. The timing generator is operated with a predesigned voltage such as 5 volts, 3.3 volts, or 2.5 volts. The operational power consumption of the timing generator under these voltages can be great. The significant power consumption and heat generation under continuous operation becomes an issue with the downsizing of circuit design.
A low power timing generator is preferred for portable devices with a limited battery capacity. The power consumption problem of a conventional timing generator must be solved for providing more efficient operation of the circuits. Further, the heat generation must be reduced at the same time to increase the reliability and life of the circuits.